This invention relates to the production of an anhydrous aluminum chloride composition and more particularly to the production of the anhydrous aluminum chloride composition from a water-based aluminous material such as an aqueous slurry of aluminum hydroxide by a multistage extraction process in which aluminum in dehydrated form is extracted into an organic liquid phase and subsequently extracted from the organic phase into a metal chloride melt. One important use of the anhydrous aluminum chloride composition is as a feedstock for an electrolysis cell in which metallic aluminum is produced from anhydrous aluminum chloride.
Traditionally, metallic aluminum has been produced by the established Bayer-Hall-Heroult process in which aluminum oxide is electrolyzed in cryolite to the metallic form. Large amounts of energy are consumed in the process. More recently a process has been developed which utilizes anhydrous aluminum choride in place of aluminum oxide and operates at a lower working temperature and a higher current density. thereby substantially reducing energy consumption.
In the electrolysis process, the bath includes a melt of mixed chlorides composed of one or more alkali metal chlorides in addition to anhydrous aluminum chloride. Typically, the aluminum chloride is present in an amount of about 5 mole %.
Anhydrous aluminum chloride for the electrolysis process is prepared by reacting aluminum oxide, carbon (from fuel oil) and chlorine gas. In addition to aluminum chloride, carbon tetrachloride and other chlorinated organics are produced which have objectionable environmental properties. Also, the process requires the use of equipment fabricated from materials resistant to the chlorine gas and these materials are often expensive. Further details related to the use of aluminum chloride and its preparation may be found in the disclosure in U.S. Pat. No. 4,252,774.
It is important that the aluminum chloride used in the electrolysis process be anhydrous and not be contaminated with water, including water of hydration. With water present, as in hydrated aluminum chloride, the chloride will be at least partially converted to the oxide thereby depleting the aluminum chloride available for producing the metallic aluminum.
One object of this invention is a process for preparing an anhydrous aluminum chloride composition at a relatively low temperature. Another object of the invention is a process of preparing an anhydrous aluminum chloride composition without a reaction involving the production of carbon tetrachlorde or other organic chlorides. A further object of this invention is a process for preparing an anhydrous aluminum chloride composition which does not involve a chlorination reaction with carbon or organic materials. Still another object of this invention is a process of preparing an aluminum chloride composition which is anhydrous and may be utilized as a feedback for an electrolysis cell for producing metallic aluminum. Yet another object of this invention is a process for preparing an anhydrous aluminum chloride composition which may be coupled to an electrolysis cell to provide a continuous source of feedstock for the cell. It is also an object to provide a process in which one or more components may be recycled. Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention.